In the electric system of motor vehicles, the electrical energy needed for the electrical supply is typically produced by generators, their output voltage being regulated to largely constant values in a predefinable manner via a voltage regulator. The battery is typically charged with this approximately constant voltage, the actual charging voltage being set via the voltage regulator such that predefinable parameters are taken into consideration. A voltage regulator that regulates according to a characteristic curve that can be dependent on different parameters, e.g. temperature, is used for this purpose. For regulation, a point is then selected on this characteristic curve, and a control voltage is set accordingly.
The value of the set voltage is restricted at the top to reduce negative effects on the battery as much as possible. In this manner, corrosion and water consumption are to be reduced to the greatest possible extent.
Modern vehicles with diverse current consumers require powerful generators allowing longer battery charging phases already at low engine speeds. In vehicle operation, the output of the generator typically covers the current requirement to the extent that no battery discharge occurs. Particularly powerful generators provide high charging currents already at low engine speeds, thereby resulting in constant battery charging.
However, when charging batteries below the gassing voltage, a concentration polarization of the electrodes results due to the built-up acid with a higher density in the pore structure. This relates to maintenance-free batteries in lead-calcium technology in particular. The counter-voltage of the battery increases as a result of these procedures, and a charging current is no longer received. The higher density acid sinks down within the cell. Since the exchange of acid directly in the pore structure of the plates of the battery with the acid reservoir between the electrodes can only occur via diffusion, exchange processes occur very slowly. The observed acid stratification, which limits the usable capacity of the battery and results in a reduction in the duration of usage time, occurs in the battery particularly in combination with discharges via high currents that mainly discharge the upper electrode portion of the battery electrodes.